1. Technical Field
The present invention relates to a resilient electrical contact element, or spring contact for making pressure contacts between electrical components. More particularly, the present invention relates to a structure used to form the spring contacts and a method of forming the spring contacts and attaching the contacts to a substrate for use in probing integrated circuits (ICs) on a wafer, or as contacts for wafer level packaging, socket contacts, or other resilient contact structure embodiments.
2. Related Art
Resilient contact elements, or spring contacts are manufactured in a variety of forms. One type of spring contacts used for probing ICs on a wafer is described in U.S. Pat. No. 5,476,211 entitled “Method of Manufacturing Electrical Contacts, Using a Sacrificial Member” and its counterpart divisional patents, U.S. Pat. No. 5,852,871, and U.S. Pat. No. 6,049,976, all by Khandros. These patents disclose methods for making resilient interconnection elements by mounting a flexible elongate core element (e.g., wire “stem” or “skeleton”) to a terminal on an electronic component and coating the flexible core element with a “shell” of one or more materials to ensure a resilient nature. Exemplary materials for the core element include gold. Exemplary materials for the resilient coating include nickel and its alloys. The resulting spring contact element is used to make pressure connections between two or more electronic components including between a probe card and ICs on a wafer.
Connection of the spring contacts to a substrate to form a probe card, or other structure is described in U.S. Pat. No. 5,974,662, entitled “Method of Planarizing Tips of Probe Elements of a Probe Card Assembly” by Eldridge, Grube, Khandros and Mathieu. This patent describes a probe card assembly including resilient spring contact elements mounted to form a “space transformer.” A space transformer is a multilayer interconnection substrate having terminals disposed at a first pitch, or spacing between terminals on one surface and having corresponding terminals disposed at a second pitch on an opposite surface. Space transformation is provided by routing lines in the layers of the substrate used to effect “pitch-spreading” from the first pitch to the second pitch. In use, the free ends (tips) of the elongate spring contact elements make pressure connections with corresponding terminals on an electronic component being probed or tested.
A more recent type of spring contact element is described in U.S. Pat. No. 6,482,013, entitled “Microelectronic Spring Contact Element and Electronic Component Having A Plurality Of Spring Contact Elements” by Eldridge, Grube, Khandros and Mathieu, incorporated herein by reference. This patent describes photo lithographic rather than mechanical techniques to fabricate resilient contact elements. As with the mechanically formed contact elements, the resilient contact elements formed using lithographic techniques include a resilient material, such as nickel and its alloys. To manufacture a probe card, or other substrate with resilient contacts using photolithographic techniques, in one embodiment the spring contacts are formed on the surface of a sacrificial substrate by a series of steps including plating or deposition of material, applying photoresist, masking using photolithographic techniques, and etching. The sacrificial substrate with spring contacts is then transferred and mounted on terminals of a space transformer. The sacrificial substrate is then removed.
In addition to being provided on a space transformer in a probe card, resilient spring contacts can also be used on an interposer of a probe card to flexibly interconnect multiple space transformer substrates. The interposer includes resilient contacts provided on both sides of a substrate.
Additionally, resilient contacts can be anchored to a pad or terminal on a number of other electronic components as described in U.S. Pat. No. 6,669,489, entitled “Interposer, socket and assembly for socketing an electronic component and method of making and using same.” The resilient contacts serve to electrically attach to a pad or terminal and be secured on one end, while maintaining electrical contact and absorbing compressive forces applied to the free end. Electronic components on which the spring contacts may be applied are described to include: the space transformer and interposer substrates described above, semiconductor wafers and dies; production interconnect sockets; test sockets; sacrificial members, elements and substrates, semiconductor packages, including ceramic and plastic packages, chip carriers; and connectors. The resilient contact is particularly beneficial when a applied to silicon dies, because they eliminate the need for having a semiconductor package.
It is desirable to continue to provide new methods of fabricating interconnection elements suitable for fine-pitch electrical connections, particularly methods that are repeatable, consistent and inexpensive.